1. Field of the Invention
The present invention relates to a method for setting channels of variable bandwidth in a mobile communication system comprising mobile stations, base stations and a base station controller. Moreover, the present invention also relates to a mobile communication system in which variable bandwidths are set in this manner, and a base station controller for setting these variable bandwidths.
2. Description of the Related Art
In the field of a mobile communication system, for instance, cellular phones, and the like, a cdma2000 (MC-CDMA) system for broadening the bandwidth of a cdmaOne system is coming into practical use.
In addition to the fundamental channel (Fch: Fundamental Channel) in the cdmaone system, the cdma2000 system newly provides a dedicated control channel (DCch) and a supplementary channel (hereinafter, called “Sch”). A communication circuit between the respective mobile stations (cellular phones, car phones, etc.) and the base station and base station controller is constituted by Fch, DCch and Sch.
Fch and DCch are jointly called the traffic channel (hereinafter, “Tch”). This traffic channel Tch is used for both voice communications, and data communications by packet transmission, or the like. The Sch, on the other hand, is used only for packet communication of data, or the like. Moreover, the Fch and DCch included in the Tch are both assigned a fixed size bandwidth (resource, rate). For example, they are assigned a 9.6 kbps bandwidth.
The Sch, on the other hand, can be assigned a bandwidth, (resource, rate) of variable size, it being possible to assign any requested bandwidth that can be guaranteed, below a predetermined maximum value. For example, at 9.6×m [kbps] (where m is a positive integer), a bandwidth up to the predetermined maximum value of 144 [kbps] (in other words, m=15), can be assigned.
If data communications are being performed between a mobile station and the base station, then generally, the Tch (either Fch or DCch) is used first, and if the Tch bandwidth is not sufficient, then the Sch is used as well. In this case, the necessary bandwidth is allocated to the Sch. Therefore, when the mobile station is only performing voice communications, or when it is performing data communications by Tch only, then only Tch is in use and Sch is not set up.
In a current cdma2000 system, the allocation of bandwidth to the Sch is performed equally for each mobile station. In other words, if the requested bandwidth can be guaranteed for each one of the mobile stations, this requested bandwidth is assigned to the Sch of those mobile stations. On the other hand, if the requested bandwidth cannot be guaranteed, then communications are continued using Tch only, without setting the Sch for the mobile stations.
Furthermore, during hand-off performed by a mobile station moving between cells or sectors, if the bandwidth of Sch set between the mobile station and the source side base station cannot be guaranteed between the mobile station and the target side base station, then the Sch between the mobile station and the target base station is not set and no hand-off is implemented for the Sch.
In this way, in the current cdma2000 system, if the bandwidth requested for the Sch cannot be guaranteed, then even if a smaller bandwidth can be guaranteed, that bandwidth is not assigned to the Sch and hence efficient use of the bandwidth (resource) is not achieved.
Furthermore, although the bandwidth usable for the Sch is limited by the maximum value 144 [kbps], any mobile station is assigned directly with the full requested bandwidth as long as the bandwidth is less than this maximum value. Consequently, situations may arise where Sch is set in some of the mobile stations, whilst no Sch at all is set in the remaining mobile stations. This in turn leads to a risk that the appeal of the service will decline.